Method of making a coated abrasive

ABSTRACT

An abrasive article includes an array of protruding abrasive units. Each unit has a base and a distal apex that is off-center from the base when projected on to a plane that is coplanar with the base. The abrasive article includes a backing bonded to an abrasive coating formed to include the aforementioned abrasive units. Methods for making the abrasive article include nipping a production tool, an abrasive slurry, and the backing. A binder within the slurry is cured during fabrication. The abrasive article may be used to abrade a workpiece.

FIELD OF THE INVENTION

This invention pertains to an abrasive array, an abrasive article, amethod of making such an abrasive article and a method of using such anabrasive article. The abrasive article comprises a backing having anabrasive coating bonded to at least one surface of the backing. Theabrasive coating is shaped to include protruding units exhibiting usefulgeometries.

BACKGROUND

Abrasive articles have been utilized to abrade and finish workpiecessurfaces for well over a hundred years. These applications have rangedfrom high stock removal, high pressure metal grinding processes to finepolishing of ophthalmic lenses. In general abrasive articles comprise aplurality of abrasive particles bonded either together (e.g., a bondedabrasive or grinding wheel) or to a backing (e.g., a coated abrasive).For a coated abrasive there is typically a single, or sometimes twolayers of abrasive particles. Once these abrasive particles are worn,the coated abrasive is essentially worn out and is typically discarded.

A structured abrasive is taught by U.S. Pat. No. 5,152,917 (Pieper etal.). Importantly, the structured abrasive taught by Peiper results in arelatively high rate of cut and a relatively fine surface finish on theworkpiece surface. The structured abrasive comprises non-random,precisely shaped abrasive composites that are bonded to a backing.

Although structured abrasives, such as the one taught by Pieper exhibitdesirable characteristics, such as a high cut rate, structured abrasivesstill tend to lose their effectiveness over time. Thus, a structuredabrasive may yield a particular cut rate (expressed, for example, ingrams per cycle) in its initial three or four cycles of abrasion, butmay yield a cut rate of only a fraction of its initial value after 5 or10 cycles. Such deterioration in cut rate is inimical to the goal ofproviding efficient abrasion technology.

As is evident from the foregoing, there exists a need for a scheme bywhich a structured abrasive may be made to prolong its life span andminimize its cut-rate deterioration.

SUMMARY

This invention pertains to an abrasive array, an abrasive article, amethod of making an abrasive article and a method of using an abrasivearticle. According to one embodiment of the present invention anabrasive array of a plurality of protruding units may be structure suchthat each unit has a body composed of at least abrasive grains and abinder. Each body may have a base and a region most distal from thebase. The abrasive array may include a plurality of protruding unitsdistributed in two dimensions. Each protruding unit has a base that hasa periphery. For each unit, its respective distal region, when projectedon to a plane that is coplanar with its respective base, defines anoffset vector between the projection of the distal region and a centerpoint of the base. The offset vectors for the plurality of protrudingunits do not exhibit a sum that approaches a limit of zero.

According to another embodiment of the invention, an abrasive articleincludes a backing having a front and back surface. An abrasive coatingmay be bonded to the front surface of the backing. The abrasive coatingmay include a plurality of protruding units distributed in twodimensions. Each protruding unit has a base that has a periphery. Foreach unit, its respective distal region, when projected on to a planethat is coplanar with its respective base, defines an offset vectorbetween the projection of the distal region and a center point of thebase. The offset vectors for the plurality of protruding units do notexhibit a sum that approaches a limit of zero.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view, enlarged, representing another abrasivearticle embodiment of this invention;

FIG. 2 is a schematic of a process of making the abrasive article ofFIG. 1; and

FIG. 3 is a schematic of another process of making the abrasive articleof FIG. 1.

FIG. 4A depicts a top view of a protruding unit in accordance with anembodiment of the present invention.

FIG. 4B depicts a top view of a protruding unit in accordance with anembodiment of the present invention.

FIG. 4C depicts a top view of an abrasive article in accordance with anembodiment of the present invention.

FIG. 4D depicts another top view of an abrasive article in accordancewith an embodiment of the present invention.

FIG. 4E depicts another top view of a protruding unit in accordance withan embodiment of the present invention.

FIG. 4F depicts another top view of a protruding unit in accordance withan embodiment of the present invention.

FIG. 4G depicts another top view of a protruding unit in accordance withan embodiment of the present invention.

FIG. 4H depicts another top view of a protruding unit in accordance withan embodiment of the present invention.

FIG. 5 depicts another abrasive article in accordance with an embodimentof the present invention.

FIG. 6A depicts an array of protruding units in accordance with anembodiment of the present invention.

FIG. 6B depicts another array of protruding units in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

This invention pertains to an abrasive array, an abrasive article, amethod of making an abrasive article and a method of using an abrasivearticle.

Referring to FIG. 1, the abrasive article 20 comprises abrasivecomposites 22 separated by boundary 25. The abrasive composites arebonded to a surface of a backing 21. The boundary or boundariesassociated with the composite shape result in one abrasive compositebeing separated to some degree from another adjacent abrasive composite.To form an individual abrasive composite, a portion of the boundariesforming the shape of the abrasive composite must be separated from oneanother. Note that in FIG. 2, the base or a portion of the abrasivecomposite closest to the backing can abut with its neighboring abrasivecomposite. Abrasive composites 22 comprise a plurality of abrasiveparticles 24 that are dispersed in a binder 23 and a grinding aid 26. Itis also within the scope of this invention to have a combination ofabrasive composites bonded to a backing in which some of the abrasivecomposites abut, while other abrasive composites have open spacesbetween them.

Backing

The backing of this invention has a front and back surface and can beany conventional abrasive backing. Examples of useful backings includepolymeric film, primed polymeric film, cloth, paper, vulcanized fiber,nonwovens, and combinations thereof. Other useful backings include afibrous reinforced thermoplastic backing as disclosed in U.S. Pat. No.5,316,812 and an endless seamless backing as disclosed in World PatentApplication No. WO 93/12911 published. The backing may also contain atreatment or treatments to seal the backing and/or modify some physicalproperties of the backing. These treatments are well known in the art.

The backing may also have an attachment means on its back surface toenable securing the resulting coated abrasive to a support pad orback-up pad. This attachment means can be a pressure sensitive adhesive,one surface of a hook and loop attachment system, or a threadedprojection as disclosed in the above-mentioned U.S. Pat. No. 5,316,812.Alternatively, there may be an intermeshing attachment system asdescribed in the assignee's U.S. Pat. No. 5,201,101 incorporated hereinafter by reference.

The backside of the abrasive article may also contain a slip resistantor frictional coating. Examples of such coatings include an inorganicparticulate (e.g., calcium carbonate or quartz) dispersed in anadhesive.

Abrasive Coating

Abrasive Particles

The abrasive particles typically have a particle size ranging from about0.1 to 1500 micrometers, usually between about 0.1 to 400 micrometers,preferably between 0.1 to 100 micrometers and most preferably between0.1 to 50 micrometers. It is preferred that the abrasive particles havea Mohs' hardness of at least about 8, more preferably above 9. Examplesof such abrasive particles include fused aluminum oxide (which includesbrown aluminum oxide, heat treated aluminum oxide and white aluminumoxide), ceramic aluminum oxide, green silicon carbide, silicon carbide,chromia, alumina zirconia, diamond, iron oxide, ceria, cubic boronnitride, boron carbide, gamet and combinations thereof.

The term “abrasive particle” also encompasses when single abrasiveparticles are bonded together to form an abrasive agglomerate. Abrasiveagglomerates are further described in U.S. Pat. Nos. 4,311,489;4,652,275 and 4,799,939 incorporated herein by reference.

It is also within the scope of this invention to have a surface coatingon the abrasive particles. The surface coating may have many differentfunctions. In some instances the surface coatings increase adhesion ofabrasive particles to the binder, alter the abrading characteristics ofthe abrasive particle, and the like. Examples of surface coatingsinclude coupling agents, halide salts, metal oxides including silica,refractory metal nitrides, refractory metal carbides and the like.

In the abrasive composite there may also be diluent particles. Theparticle size of these diluent particles may be on the same order ofmagnitude as the abrasive particles. Examples of such diluent particlesinclude gypsum, marble, limestone, flint, silica, glass bubbles, glassbeads, aluminum silicate, and the like.

Binder

The abrasive particles are dispersed in an organic binder to form theabrasive composite. The binder is derived from a binder precursor whichcomprises an organic polymerizable resin. During the manufacture of theinventive abrasive articles, the binder precursor is exposed to anenergy source which aids in the initiation of the polymerization orcuring process. Examples of energy sources include thermal energy andradiation energy, the latter including electron beam, ultraviolet light,and visible light. During this polymerization process, the resin ispolymerized and the binder precursor is converted into a solidifiedbinder. Upon solidification of the binder precursor, the abrasivecoating is formed. The binder in the abrasive coating is also generallyresponsible for adhering the abrasive coating to the backing.

There are two preferred classes of resins for use in the presentinvention, condensation curable and addition polymerizable resins. Thepreferred binder precursors comprise additional polymerizable resinsbecause these resins are readily cured by exposure to radiation energy.Addition polymerizable resins can polymerize through a cationicmechanism or a free radical mechanism. Depending upon the energy sourcethat is utilized and the binder precursor chemistry, a curing agent,initiator, or catalyst is sometimes preferred to help initiate thepolymerization.

Examples of typical and preferred organic resins include phenolicresins, urea-formaldehyde resins, melamine formaldehyde resins,acrylated urethanes, acrylated epoxies, ethylenically unsaturatedcompounds, aminoplast derivatives having pendant unsaturated carbonylgroups, isocyanurate derivatives having at least one pendant acrylategroup, isocyanate derivatives having at least one pendant acrylategroup, vinyl ethers, epoxy resins, and mixtures and combinationsthereof. The term “acrylate” encompasses acrylates and methacrylates.

Phenolic resins are widely used in abrasive article binders because oftheir thermal properties, availability, and cost. There are two types ofphenolic resins, resole and novolac. Resole phenolic resins have a molarratio of formaldehyde to phenol of greater than or equal to one to one,typically between 1.5:1.0 to 3.0:1.0. Novolac resins have a molar ratioof formaldehyde to phenol of less than one to one. Examples ofcommercially available phenolic resins include those known by the tradenames “Durez” and “Varcum” from Occidental Chemicals Corp.; “Resinox”from Monsanto; “Aerofene” from Ashland Chemical Co. and “Aerotap” fromAshland Chemical Co.

Acrylated urethanes are diacrylate esters of hydroxy-terminated,isocyanate NCO extended polyesters or polyethers. Examples ofcommercially available acrylated urethanes include those known under thetrade designations “UVITHANE 782”, available from Morton ThiokolChemical, and “CMD 6600”, “CMD 8400”, and “CMD 8805”, available fromRadcure Specialties.

Acrylated epoxies are diacrylate esters of epoxy resins, such as thediacrylate esters of bisphenol A epoxy resin. Examples of commerciallyavailable acrylated epoxies include those known under the tradedesignations “CMD 3500”, “CMD 3600”, and “CMD 3700”, available fromRadcure Specialities.

Ethylenically unsaturated resins include both monomeric and polymericcompounds that contain atoms of carbon, hydrogen, and oxygen, andoptionally, nitrogen and the halogens. Oxygen or nitrogen atoms or bothare generally present in ether, ester, urethane, amide, and urea groups.

Ethylenically unsaturated compounds preferably have a molecular weightof less than about 4,000 and are preferably esters made from thereaction of compounds containing aliphatic monohydroxy groups oraliphatic polyhydroxy groups and unsaturated carboxylic acids, such asacrylic acid, methacrylic acid, itaconic acid, crotonic acid,isocrotonic acid, maleic acid, and the like. Representative examples ofacrylate resins include methyl methacrylate, ethyl methacrylate styrene,divinylbenzene, vinyl toluene, ethylene glycol diacrylate, ethyleneglycol methacrylate, hexanediol diacrylate, triethylene glycoldiacrylate, trimethylolpropane triacrylate, glycerol triacrylate,pentaerythritol triacrylate, pentaerythritol methacrylate,pentaerythritol tetraacrylate and pentaerythritol tetraacrylate. Otherethylenically unsaturated resins include monoallyl, polyallyl, andpolymethallyl esters and amides of carboxylic acids, such as diallylphthalate, diallyl adipate, and N,N-diallyladkipamide. Still othernitrogen containing compounds includetris(2-acryloyloxyethyl)isocyanurate,1,3,5-tri(2-methyacryloxyethyl)-triazine, acrylamide, methylacrylamide,N-methylacrylamide, N,N-dimethylacrylamide, N-vinylpyrrolidone, andN-vinylpiperidone.

The aminoplast resins have at least one pendant alpha, betaunsaturatedcarbonyl group per molecule or oligomer. These unsaturated carbonylgroups can be acrylate, methacrylate, or acrylamide type groups.Examples of such materials include N-(hydroxymethyl)acrylamide,N,N′-oxydimethylenebisacrylamide, ortho and para acrylamidomethylatedphenol, acrylamidomethylated phenolic novolac, and combinations thereof.These materials are further described in U.S. Pat. Nos. 4,903,440 and5,236,472 both incorporated herein by reference.

Isocyanurate derivatives having at least one pendant acrylate group andisocyanate derivatives having at least one pendant acrylate group arefurther described in U.S. Pat. No. 4,652,274 incorporated herein afterby reference. The preferred isocyanurate material is a triacrylate oftris(hydroxy ethyl) isocyanurate.

Epoxy resins have an oxirane and are polymerized by the ring opening.Such epoxide resins include monomeric epoxy resins and oligomeric epoxyresins. Examples of some preferred epoxy resins include2,2-bis[4-(2,3-epoxypropoxy)-phenyl propane] (diglycidyl ether ofbisphenol) and commercially available materials under the tradedesignations “Epon 828”, “Epon 1004”, and “Epon 1001F” available fromShell Chemical Co., “DER-331”, “DER-332”, and “DER-334” available fromDow Chemical Co. Other suitable epoxy resins include glycidyl ethers ofphenol formaldehyde novolac (e.g., “DEN-431” and “DEN-428” availablefrom Dow chemical Co.).

The epoxy resins of the invention can polymerize via a cationicmechanism with the addition of an appropriate cationic curing agent.Cationic curing agents generate an acid source to initiate thepolymerization of an epoxy resin. These cationic curing agents caninclude a salt having an onium cation and a halogen containing a complexanion of a metal or metalloid. Other cationic curing agents include asalt having an organometallic complex cation and a halogen containingcomplex anion of a metal or metalloid which are further described inU.S. Pat. No. 4,751,138 incorporated here in after by reference (column6, line 65 to column 9, line 45). Another example is an organometallicsalt and an onium salt is described in U.S. Pat. No. 4,985,340 (column4, line 65 to column 14, line 50); and European Patent Application Nos.306,161 and 306,162, both published Mar. 8, 1989, all incorporated byreference. Still other cationic curing agents include an ionic salt ofan organometallic complex in which the metal is selected from theelements of Periodic Group IVB, VB, VIB, VIIB and VIIB which isdescribed in European Patent Application No. 109,581, published Nov. 21,1983, incorporated by reference.

Regarding free radical curable resins, in some instances it is preferredthat the abrasive slurry further comprises a free radical curing agent.However in the case of an electron beam energy source, the curing agentis not always required because the electron beam itself generates freeradicals.

Examples of free radical thermal initiators include peroxides, e.g.,benzoyl peroxide, azo compounds, benzophenones, and quinones. For eitherultraviolet or visible light energy source, this curing agent issometimes referred to as a photoinitiator. Examples of initiators, thatwhen exposed to ultraviolet light generate a free radical source,include but are not limited to those selected from the group consistingof organic peroxides, azo compounds, quinones, benzophenones, nitrosocompounds, acryl halides, hydrozones, mercapto compounds, pyryliumcompounds, triacrylimdazoles, bisimidazoles, chloroalkytriazines,benzoin ethers, benzil ketals, thioxanthones, and acetophenonederivatives, and mixtures thereof. Examples of initiators that whenexposed to visible radiation generate a free radical source, can befound in U.S. Pat. No. 4,735,632, entitled Coated Abrasive BinderContaining Ternary Photoinitiator System, incorporated herein byreference. The preferred initiator for use with visible light is“Irgacure 369” commercially available from Ciba Geigy Corporation.

Grinding Aid

A grinding aid is defined as a material, preferably a particulatematerial, the addition of which to an abrasive article has a significanteffect on the chemical and physical processes of abrading which resultsin improved performance. Typically and preferably the grinding aid isadded to the slurry as a particulate, however it may be added to theslurry as a liquid. The presence of the grinding aid will increase thegrinding efficiency or cut rate (defined as weight of work piece removedper weight of abrasive article lost) of the corresponding abrasivearticle in comparison to an abrasive article that does not contain agrinding aid. In particular, it is believed in the art that the grindingaid will either 1) decrease the friction between the abrasive grains andthe workpiece being abraded, 2) prevent the abrasive grain from“capping”, i.e., prevent metal particles (in the case of a metalworkpiece) from becoming welded to the tops of the abrasive grains, 3)decrease the interface temperature between the abrasive grains theworkpiece, 4) decreases the grinding force required, or 5) preventsoxidation of the metal workpiece. In general, the addition of a grindingaid increases the useful life of the abrasive article.

Grinding aids useful in the invention encompass a wide variety ofdifferent materials and can be inorganic or organic based. Examples ofchemical groups of grinding aids include waxes, organic halidecompounds, halide salts and metals and their alloys. The organic halidecompounds will typically break down during abrading and release ahalogen acid or a gaseous halide compound. Examples of such materialsinclude chlorinated waxes like tetrachloronaphtalene,pentachloronaphthalene; and polyvinyl chloride. Examples of halide saltsinclude sodium chloride, potassium cryolite, sodium cryolite, ammoniumcryolite, potassium tetrafluoroborate, sodium tetrafluoroborate, siliconfluorides, potassium chloride, magnesium chloride. Examples of metalsinclude, tin, lead, bismuth, cobalt, antimony, cadmium, iron titanium,other miscellaneous grinding aids include sulfur, organic sulfurcompounds, graphite and metallic sulfides. It is also within the scopeof this invention to use a combination of different grinding aids and insome instances this may produce a synergistic effect.

The above-mentioned examples of grinding aids are meant to berepresentative only. A preferred grinding aid for use in the inventionis cryolite, and the most preferred is potassium tetrafluoroborate(KBF.sub.4).

The grinding aid is considered to be non-abrasive, that is, the Mohhardness of the grinding aid is less than 8. The grinding aid may alsocontain impurities; these impurities should not significantly adverselyaffect performance of the abrasive article.

The grinding aid particle size preferably ranges from about 0.1 to 100micrometers, more preferably between 10 to 70 micrometers. In generalthe particle size of the grinding aid is preferably equal to or lessthan the size of the abrasive particles.

The abrasive coating comprises generally at least about 1% by weight,typically at least about 2.5% by weight, preferably at least about 5% byweight, more preferably at least about 10% by weight grinding aid andmost preferably at least about 20% by weight grinding aid. More thanabout 50 weight % grinding aid may be detrimental since it is theorizedthat grinding performance would decrease (since there are less abrasiveparticles present). It was surprising that as the amount of grinding aidwas increased, the relative grinding performance as measured by cut rateis also increased. This was unexpected since as the amount of grindingaid in the abrasive coating is increased, the relative amount ofabrasive particles is decreased. The abrasive particles are responsiblefor cutting the workpiece surface, not the grinding aid. In general, theabrasive coating comprises from 5 to 90% by weight, preferably from 20to 80% by weight abrasive particles, from 5 to 80% by weight, preferablyfrom 5 to 40% by weight binder, and from 5 to 60% by weight, preferablyfrom 10 to 40% by weight grinding aid.

Optional Additives

Slurries useful in the invention may further comprise optionaladditives, such as, for example, fillers, fibers, lubricants, wettingagents, thixotropic materials, surfactants, pigments, dyes, antistaticagents, coupling agents, plasticizers, and suspending agents. Theamounts of these materials are selected to provide the propertiesdesired. The use of these can affect the erodability of the abrasivecomposite. In some instances an additive is purposely added to make theabrasive composite more erodable, thereby expelling dulled abrasiveparticles and exposing new abrasive particles.

Examples of antistatic agents useful in the invention include graphite,carbon black, vanadium oxide, humectants, and the like. These antistaticagents are disclosed in U.S. Pat. Nos. 5,061,294; 5,137,542, and5,203,884 incorporated herein after by reference.

A coupling agent can provide an association bridge between the binderprecursor and the filler particles or abrasive particles. Examples ofuseful coupling agents include silanes, titanates, and zircoaluminates.Useful slurries preferably contain from about 0.01 to 3% by weightcoupling agent.

An example of a suspending agent useful in the invention is an amorphoussilica particle having a surface area less than 150 meters square/gramthat is commercially available from DeGussa Corp., under the trade name“OX-50”.

Abrasive Coating Comprising Abrasive Composites

In one preferred aspect of the invention, the abrasive coating is in theform of a plurality of abrasive composites bonded to the backing. It isgenerally preferred that each abrasive composites have a precise shape.The precise shape of each composite is determined by distinct anddiscernible boundaries. These distinct and discernible boundaries arereadily visible and clear when a cross section of the abrasive articleis examined under a microscope such as a scanning electron microscope.In comparison, in an abrasive coating comprising composites that do nothave precise shapes, the boundaries are not definitive and may beillegible. These distinct and discernible boundaries form the outline orcontour of the precise shape. These boundaries separate to some degreeone abrasive composite from another and also distinguish one abrasivecomposite from another.

Referring to FIG. 1, the abrasive article 10 comprises abrasivecomposites 22 separated by boundary 25. The boundary or boundariesassociated with the composite shape result in one abrasive compositebeing separated to some degree from another adjacent abrasive composite.To form an individual abrasive composite, a portion of the boundariesforming the shape of the abrasive composite must be separated from oneanother. Note that in FIG. 1, the base or a portion of the abrasivecomposite closest to the backing can abut with its neighboring abrasivecomposite. Abrasive composites 22 comprise a plurality of abrasiveparticles 24 that are dispersed in a binder 23 and a grinding aid 26. Itis also within the scope of this invention to have a combination ofabrasive composites bonded to a backing in which some of the abrasivecomposites abut, while other abrasive composites have open spacesbetween them.

In some instances the boundaries forming the shape are planar. Forshapes that have planes, there are at least three planes. The number ofplanes for a given shape can vary depending upon the desired geometry,for instance the number of planes can range from three to over 20.Generally, there are between three to ten planes, preferably betweenthree to six planes. These planes intersect to form the desired shapeand the angles at which these planes intersect will determine the shapedimensions.

In another aspect of this invention, a portion of the abrasivecomposites have a neighboring abrasive composite of a differentdimension. In this aspect of the invention, at least 10%, preferably atleast 30%, more preferably at least 50% and most preferably at least 60%of the abrasive composites have an adjacent abrasive composite that hasa different dimension. These different dimensions can pertain to theabrasive composite shape, angle between planar boundaries or dimensionsof the abrasive composite. The result of these different dimensions forneighboring abrasive composites results in an abrasive article thatproduces a relatively finer surface finish on the workpiece beingabraded or refined. This aspect of the invention is further described inthe assignee's co-pending patent application U.S. Ser. No. 08/120,300filed Sep. 13, 1993.

The abrasive composite shape can be any shape, but it is preferably ageometric shape such as a rectangle, cone, semicircle, circle, triangle,square, hexagon, pyramid, octagon and the like. Embodiments of preferredshapes are presented below in a section entitled “GEOMETRIES.” Anindividual abrasive composite shape may be referred to herein as a“protruding unit.” The preferred shape is a pyramid and the base of thispyramid can be a three or four sided. It is also preferred that theabrasive composite cross sectional surface area decreases away from thebacking or decreases along its height. This variable surface arearesults in a non-uniform pressure as the abrasive composite wears duringuse. Additionally, during manufacture of the abrasive article, thisvariable surface area results in easier release of the abrasivecomposite from the production tool. In general there are at least 5individual abrasive composites per square cm. In some instances, theremay be at least 500 individual abrasive composites/square cm.

Method of Making the Abrasive Article

An essential step to make any of the inventive abrasive articles is toprepare the slurry. The slurry is made by combining together by anysuitable mixing technique the binder precursor, the grinding aid, theabrasive particles and the optional additives. Examples of mixingtechniques include low shear and high shear mixing, with high shearmixing being preferred. Ultrasonic energy may also be utilized incombination with the mixing step to lower the abrasive slurry viscosity.Typically, the abrasive particles and grinding aid are gradually addedinto the binder precursor. The amount of air bubbles in the slurry canbe minimized by pulling a vacuum during the mixing step. In someinstances it is preferred to heat, generally in the range of 30° to 70°C., the slurry to lower the viscosity. It is important the slurry havetheological properties that allow the slurry to coat well and in whichthe abrasive particles and grinding aid do not settle out of the slurry.

Energy Source

After the slurry is coated onto the backing, such as via transfer from aproduction tool (discussed below), the slurry may be exposed to anenergy source to initiate the polymerization of the resin in the binderprecursor. Examples of energy sources include thermal energy andradiation energy. The amount of energy depends upon several factors suchas the binder precursor chemistry, the dimensions of the abrasiveslurry, the amount and type of abrasive particles and the amount andtype of the optional additives. For thermal energy, the temperature canrange from about 30° to 150° C., generally from 40° to 120° C. Theexposure time can range from about 5 minutes to over 24 hours.

Suitable radiation energy sources include electron beam, ultravioletlight, or visible light. Electron beam radiation, which is also known asionizing radiation, can be used at an energy level of about 0.1 to about10 Mrad, preferably at an energy level of about 1 to about 10 Mrad.Ultraviolet radiation refers to non-particulate radiation having awavelength within the range of about 200 to about 400 nanometers,preferably within the range of about 250 to 400 nanometers. Visibleradiation refers to non-particulate radiation having a wavelength withinthe range of about 400 to about 800 nanometers, preferably in the rangeof about 400 to about 550 nanometers. It is preferred that 300 to 600Watt/inch visible lights are used.

After this polymerization process is complete, the binder precursor isconverted into a binder and the slurry is converted into an abrasivecoating. The resulting abrasive article is generally ready for use.However, in some instances other processes may still be necessary suchas humidification or flexing. The abrasive article can be converted intoany desired form such as a cone, endless belt, sheet, disc, and thelike, before the abrasive article is used.

Production Tool

Regarding the third and fourth aspects of the invention, in someinstances it is preferred that the abrasive coating be present asprecisely shaped abrasive composites. In order to make this type ofabrasive article, a production tool is generally required.

The production tool contains a plurality of cavities. These cavities areessentially the inverse shape of the abrasive composite and areresponsible for generating the shape of the abrasive composites. Thedimensions of the cavities are selected to provide the desired shape anddimensions of the abrasive composites. If the shape or dimensions of thecavities are not properly fabricated, the resulting production tool willnot provide the desired dimensions for the abrasive composites.

The cavities can be present in a dot like pattern with spaces betweenadjacent cavities or the cavities can butt up against one another. It ispreferred that the cavities butt up against one another. Additionally,the shape of the cavities is selected such that the cross-sectional areaof the abrasive composite decreases away from the backing.

The production tool can be a belt, a sheet, a continuous sheet or web, acoating roll such as a rotogravure roll, a sleeve mounted on a coatingroll, or die. The production tool can be composed of metal, (e.g.,nickel), metal alloys, or plastic. The metal production tool can befabricated by any conventional technique such as engraving, bobbing,electroforming, diamond turning, and the like. One preferred techniquefor a metal production tool is diamond turning.

A thermoplastic tool can be replicated off a metal master tool. Themaster tool will have the inverse pattern desired for the productiontool. The master tool can be made in the same manner as the productiontool. The master tool is preferably made out of metal, e.g., nickel andis diamond turned. The thermoplastic sheet material can be heated andoptionally along with the master tool such that the thermoplasticmaterial is embossed with the master tool pattern by pressing the twotogether. The thermoplastic can also be extruded or cast onto the mastertool and then pressed. The thermoplastic material is cooled to solidifyand produce the production tool. Examples of preferred thermoplasticproduction tool materials include polyester, polycarbonates, polyvinylchloride, polypropylene, polyethylene and combinations thereof. If athermoplastic production tool is utilized, then care must be taken notto generate excessive heat that may distort the thermoplastic productiontool.

The production tool may also contain a release coating to permit easierrelease of the abrasive article from the production tool. Examples ofsuch release coatings for metals include hard carbide, nitrides orborides coatings. Examples of release coatings for thermoplasticsinclude silicones and fluorochemicals.

One method to make the abrasive article of the invention illustrated inFIG. 2 is illustrated in FIG. 2. Backing 41 leaves an unwind station 42and at the same time the production tool 46 leaves an unwind station 45.Production tool 46 is coated with slurry by means of coating station 44.It is possible to heat the slurry and/or subject the slurry toultrasonics prior to coating to lower the viscosity. The coating stationcan be any conventional coating means such as drop die coater, knifecoater, curtain coater, vacuum die coater or a die coater. Duringcoating the formation of air bubbles should be minimized. The preferredcoating technique is a vacuum fluid bearing die, such as disclosed inU.S. Pat. Nos. 3,594,865, 4,959,265, and 5,077,870, all incorporatedherein by reference. After the production tool is coated, the backingand the slurry are brought into contact by any means such that theslurry wets the front surface of the backing. In FIG. 2, the slurry isbrought into contact with the backing by means of contact nip roll 47.Next, contact nip roll 47 also forces the resulting construction againstsupport drum 43. A source of energy 48 (preferably a source of visiblelight) transmits a sufficient amount of energy into the slurry to atleast partially cure the binder precursor. The term partial cure ismeant that the binder precursor is polymerized to such a state that theslurry does not flow from an inverted test tube. The binder precursorcan be fully cured once it is removed from the production tool by anyenergy source. Following this, the production tool is rewound on mandrel49 so that the production tool can be reused again. Optionally, theproduction tool may be removed from the binder precursor prior to anycuring of the precursor at all. After removal, the precursor may becured, and the production tool may be rewound on mandrel 49 for reuse.Additionally, abrasive article 120 is wound on mandrel 121. If thebinder precursor is not fully cured, the binder precursor can then befully cured by either time and/or exposure to an energy source.Additional steps to make abrasive articles according to this firstmethod are further described in U.S. Pat. No. 5,152,917 and U.S. Ser.No. 08/004,929, filed Jan. 14, 1993, both incorporated herein byreference. Randomly shaped abrasives composites may be made by thetooling and procedures described in copending Ser. No. 08/120,300, filedSep. 13, 1993, incorporated herein by reference.

It is preferred that the binder precursor is cured by radiation energy.The radiation energy can be transmitted through the production tool solong as the production tool does not appreciably absorb the radiationenergy. Additionally, the radiation energy source should not appreciablydegrade the production tool. It is preferred to use a thermoplasticproduction tool and ultraviolet or visible light.

The slurry can be coated onto the backing and not into the cavities ofthe production tool. The slurry coated backing is then brought intocontact with the production tool such that the slurry flows into thecavities of the production tool. The remaining steps to make theabrasive article are the same as detailed above.

Another method is illustrated in FIG. 3. Backing 51 leaves an unwindstation 52 and the slurry 54 is coated into the cavities of theproduction tool 55 by means of the coating station 53. The slurry can becoated onto the tool by any one of many techniques such as drop diecoating, roll coating, knife coating, curtain coating, vacuum diecoating, or die coating. Again, it is possible to heat the slurry and/orsubject the slurry to ultrasonics prior to coating to lower theviscosity. During coating the formation of air bubbles should beminimized. Then, the backing and the production tool containing theabrasive slurry are brought into contact by a nip roll 56 such that theslurry wets the front surface of the backing. Next, the binder precursorin the slurry is at least partially cured by exposure to an energysource 57. After this at least partial cure, the slurry is converted toan abrasive composite 59 that is bonded or adhered to the backing. Theresulting abrasive article is removed from the production tool by meansof nip rolls 58 and wound onto a rewind station 60. Optionally, theproduction tool may be removed from the binder precursor prior to anycuring of the precursor at all. After removal of the production tool,the precursor may be cured. In either event, the energy source can bethermal energy or radiation energy. If the energy source is eitherultraviolet light or visible light, it is preferred that the backing betransparent to ultraviolet or visible light. An example of such abacking is polyester backing.

The slurry can be coated directly onto the front surface of the backing.The slurry coated backing is then brought into contact with theproduction tool such that the slurry wets into the cavities of theproduction tool. The remaining steps to make the abrasive article arethe same as detailed above.

Method of Refining a Workpiece Surface

Another aspect of this invention pertains to a method of abrading ametal surface. This method involves bringing into frictional contact theabrasive article of this invention with a workpiece having a metalsurface. The term “abrading” means that a portion of the metal workpieceis cut or removed by the abrasive article. Additionally, the surfacefinish associated with the workpiece surface is typically reduced afterthis refining process. One typical surface finish measurement is Ra; Rais the arithmetic surface finish generally measured in microinches ormicrometers. The surface finish can be measured by a profilometer, suchas a Perthometer or Surtronic.

Workpiece

The metal workpiece can be any type of metal such as mild steel,stainless steel, titanium, metal alloys, exotic metal alloys and thelike. The workpiece may be flat or may have a shape or contourassociated with it.

Depending upon the application, the force at the abrading interface canrange from about 0.1 kg to over 1000 kg. Generally this range is from 1kg to 500 kg of force at the abrading interface. Also depending upon theapplication, there may be a liquid present during abrading. This liquidcan be water and/or an organic compound. Examples of typical organiccompounds include lubricants, oils, emulsified organic compounds,cutting fluids, soaps, or the like. These liquids may also contain otheradditives such as defoamers, degreasers, corrosion inhibitors, or thelike. The abrasive article may oscillate at the abrading interfaceduring use. In some instances, this oscillation may result in a finersurface on the workpiece being abraded.

The abrasive articles of the invention can be used by hand or used incombination with a machine. At least one or both of the abrasive articleand the workpiece is moved relative to the other during grinding. Theabrasive article can be converted into a belt, tape roll, disc, sheet,and the like. For belt applications, the two free ends of an abrasivesheet are joined together and a splice is formed. It is also within thescope of this invention to use a spliceless belt like that described inthe assignee's co-pending patent application U.S. Ser. No. 07/919,541,filed Jul. 24, 1992, incorporated herein after by reference. Generallythe endless abrasive belt traverses over at least one idler roll and aplaten or contact wheel. The hardness of the platen or contact wheel isadjusted to obtain the desired rate of cut and workpiece surface finish.The abrasive belt speed depends upon the desired cut rate and surfacefinish. The belt dimensions can range from about 5 mm to 1,000 mm wideand from about 5 mm to 10,000 mm long. Abrasive tapes are continuouslengths of the abrasive article. They can range in width from about 1 mmto 1,000 mm, generally between 5 mm to 250 mm. The abrasive tapes areusually unwound, traverse over a support pad that forces the tapeagainst the workpiece and then rewound. The abrasive tapes can becontinuously feed through the abrading interface and can be indexed. Theabrasive disc can range from about 50 mm to 1,000 mm in diameter.Typically abrasive discs are secured to a back-up pad by an attachmentmeans. These abrasive discs can rotate between 100 to 20,000 revolutionsper minute, typically between 1,000 to 15,000 revolutions per minute.

Geometries

As alluded to in the section of this disclosure entitled “ABRASIVECOATING COMPRISING ABRASIVE COMPOSITES,” the abrasive composites may beshaped into units that protrude from the backing to which they arebonded. The individual shaped composite abrasives are referred to hereinas “protruding units.” The particular geometry chosen for the protrudingunits may impact the performance of the structured abrasive article inwhich they are situated. The geometry schemes presented below are chosento provide elevated initial cut rates (as measured in mass per cycle)and to exhibit minimal deterioration in cut rates with each successiveabrasion cycle.

The protruding units shown in FIGS. 4A-H, 5, and 6A and 6B, and theother protruding units discussed herein may be structured from materialsdescribed above, making use of fabrication methods described above.Although FIGS. 4A-H, 5, and 6A and 6B do not depict abrasive grains andbinder within the protruding units, it is understood that such grainsand binder exist, as the protruding units have abrasive grains andbinder as a constituent material.

FIG. 4A depicts a top view of a protruding unit 400. The protruding unithas a base 401, which is in the shape of a square. Other than the base401, the protruding unit 400 has four sides, which extend from each ofthe various sides of the base 401 to a linear apex 406. Due to theperspective of FIG. 4A, only sides 403 and 405 are visible.

As can be seen from FIG. 4A, the linear apex 406, when projected on to aplain that is coplanar with the base 401, extends between oppositelydisposed sides of the base 401. When referring to the projection of anapex, such as apex 406, on to a plain that is coplanar with a base of aprotruding unit, the terms “projection of the apex” or “projection ofthe linear apex” may be used herein. The center points of the oppositelydisposed sides between which the projection of the linear apex 406extends are identified with small hashings. The projection of the linearapex 406 does not extend between the center points of the oppositelydisposed sides.

The protruding unit of FIG. 4A may be arranged into a two-dimensionalarray, as shown in FIG. 4B. FIG. 4B depicts an array of substantiallyidentical protruding units 400 disposed such that the base of eachprotruding unit 400 abuts the base of an adjacent protruding unit 400.The protruding units 400 are shown as being bonded to a backing 408,creating an abrasive article. Although the array depicted in FIG. 4B isshown as being two-by-two, the array may be of any size in principle.Furthermore, as shown in FIG. 4C, the array may be constructed so thatthe bases of adjacent protruding units 400 do not abut one another.

FIG. 4D depicts a protruding unit 410. As can be seen therein, theprotruding unit has a linear apex 412 that has a length that isinsufficient for its projection to extend from one side of the base 414to the other. Thus, each of the sides tapers inwardly from the base 414toward the distal linear apex. Notably, if the projection of the linearapex 412 is extrapolated, its extrapolation does not meet with a centerpoint of either oppositely disposed side of the base 414. In this way,it can be said that the projection of the linear apex 412 does notextend “between” center points of oppositely disposed sides of the base414.

FIG. 4E depicts yet another protruding unit 416. The protruding unitsdepicted in FIGS. 4A, 4B, 4C, and 4D exhibit the characteristic thattheir respective linear apexes 412 do not extend between center pointsof oppositely disposed sides of their respective bases via employment ofa similar scheme: the linear apexes have been askew to all of the sidesof their respective bases. As shown in FIG. 4E, the projection of thelinear apex 418 may be parallel to some of the sides of the base 420,and yet not extend between center points of oppositely disposed sides ofthe base 420.

FIG. 4F depicts yet another protruding unit 422. FIG. 4F demonstratesthat while the apex of a protruding unit may be linear, it is notessential that it be rectilinear. The protruding unit 422 has acurvilinear (as opposed to rectilinear) apex 424. The projection of thecurvilinear apex 424 does not extend between center points of oppositelydisposed sides of the base 426.

The bases that have been presented in FIGS. 4A, 4B, 4C, 4D, 4E, and 4Fhave all been in the shape of a square. Such a restriction is notessential. In principle, the base may be any closed shape. For example,the base may be any regular or irregular polygon, may be aparallelogram, rectangle, or any for of quadrilateral. The base may becircular or elliptical. The sides of the base may be rectilinear orcurvilinear. For example, the protruding unit 428 depicted in FIG. 4Ghas four sides, two of which are curvilinear 430 and 432. The centerpoint of the oppositely disposed curvilinear sides of the base may befound by dividing the curvilinear sides into two segments, wherein thelength of the first segment is equal to the length of the secondsegment. For example, side 430 has been divided into two segments:segments AB and BC. Point B, the center point, is positioned so that thelength of segment AB is equal to the length of segment BC. One skilledin the art understands that other measures of centrality may be used toidentify the center point of a line that is not rectilinear. Again, theprojection of the linear apex 434 extends between oppositely disposedsides 430 and 432, but not at their respective center points.

FIG. 4H depicts a protruding unit 436 that has a base 438 that is in theshape of a pentagon. The center point of side AB is identified with asmall hash mark. Notably, protruding unit 436 does not, at first glance,appear to have a side disposed opposite of side AB. For the sake oforienting the linear apex 440 so as to extend between non-central pointson oppositely disposed sides of a base, one may consider the sideopposite AB to be the compound segment ACDEB. The center point of sideACDEB is point D, because the length of segment ACD equals the length ofsegment DEB. Thus, it is plain to see that linear apex 440 does notextend between center point of oppositely disposed sides of the base438.

The general principle to be extracted from the discussion associatedwith FIG. 4H is that a particular scheme can be used to find a side thatis disposed opposite a given side of a base. In short, a set of sidesthat subtends a given side of a base may collectively be considered asingle side that is disposed opposite the given side (e.g., side ACDEBsubtends side AB, and may be considered to be disposed opposite sideAB).

FIG. 5 depicts a perspective view of an abrasive article 500 including atwo dimensional array of protruding units, some of which have beenidentified with reference numeral 502. Each protruding unit 502 has abase that is rectangular. According to one embodiment of the presentinvention, the length and width of the base may be between 1 and 150mils. Each base has a linear apex 504. According to one embodiment ofthe present invention, the linear apex may be oriented up to 60 milsabove the base. Although each of the bases in FIG. 5 is depicted ashaving the same size and geometry, neither condition is essential. Thebases may be of varying size and/or geometry. Also, although each of thelinear apexes 504 is depicted as being parallel with one another, thiscondition is not essential. The linear apexes 504 may be non-parallel toone another. Finally, although each of the linear apexes is depicted asbeing a constant distance from their respective bases, this condition isalso not essential. The distance between the bases and their respectivelinear apexes 504 may vary from protruding unit 502 to protruding unit502.

FIG. 6A depicts an array of protruding units 600-606. Each of theprotruding units 600-606 has an apex 608-614 that is substantially inthe shape of a point. Any of the linear apexes in any of the precedingexamples may be embodied as a point, as opposed to being embodied as alinear segment. Returning the discussion to FIG. 6A, in each of theprotruding units 600-606, the apex 608-614 is located remote from thecenter. The projection of each apex 608-614 defines an offset vector v₁,v₂, v₃, and v₄ extending from the center and/or center of mass of therespective base to the projection of the apex 608-614. Notably, the sumof the offset vectors v₁, v₂, v₃, and v₄ does not equal zero. Forexample, assuming that each of the offset vectors v₁, v₂, v₃, and v₄ isa unit vector, the sum of the vectors is 2y. For a large array ofprotruding units, the sum of the offset vectors should not approach alimit of zero as the number of vectors summed together approachesinfinity:lim _(n→∞)(Σν_(n))≠0Stated another way, when viewed in totality, the array should exhibitnet directionality with respect to the positioning of the apexes608-614.

FIG. 6B shows the idea of net proportionality as it applies toprotruding units having linear apexes 616-622. As can be seen from FIG.6B, the projection of the linear apexes 616-622 define an offset vectorv₁, v₂, v₃, and v₄ extending from the centers and/or centers of mass ofthe respective base to the center of the projection of the apexes616-622. Once again, for a large array of protruding units, the sum ofthe offset vectors should not approach a limit of zero as the number ofvectors summed together approaches infinity:lim _(n→∞)(Σν_(n))≠0Stated another way, when viewed in totality, the array should exhibitnet directionality with respect to the positioning of the apexes608-614.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

1. An abrasive array of a plurality of protruding units, each unithaving a body composed of at least abrasive grains and a binder, eachbody having a base and a region most distal from the base, the abrasivearray comprising: a plurality of protruding units distributed in twodimensions, wherein each protruding unit has a base that has aperiphery, wherein, for each unit, its respective distal region, whenprojected on to a plane that is coplanar with its respective base, fallswithin the periphery of the base, and defines an offset vector betweenthe projection of the distal region and a center point of the base; andwherein the offset vectors for the plurality of protruding units do notexhibit a sum that approaches a limit of zero.
 2. The abrasive array ofclaim 1, wherein each distal region is linear.
 3. The abrasive array ofclaim 2, wherein each distal region is rectilinear.
 4. The abrasivearray of claim 2, wherein each linear region is curvilinear.
 5. Theabrasive array of claim 1, wherein each base is a parallelogram.
 6. Theabrasive array of claim 5, wherein none of the sides of theparallelogram is parallel to an edge of an article upon which theabrasive array is disposed.
 7. The abrasive array of claim 1, whereinfor each unit, its respective distal region, when projected on to aplane that is coplanar with its respective base, falls within theperiphery of the base.
 8. The abrasive array of claim 1, whereinconsecutive bases do not abut.
 9. An abrasive article comprising: abacking having a front and back surface; and an abrasive coating bondedto the front surface of the backing, wherein the abrasive coatingincludes a plurality of protruding units distributed in two dimensions,wherein each protruding unit has a base that has a periphery, wherein,for each unit, its respective distal region, when projected on to aplane that is coplanar with its respective base, falls within theperiphery of the base, and defines an offset vector between theprojection of the distal region and a center point of the base; andwherein the offset vectors for the plurality of protruding units do notexhibit a sum that approaches a limit of zero.
 10. The abrasive articleof claim 9, wherein each distal region is linear.
 11. The abrasivearticle of claim 10, wherein each distal region is rectilinear.
 12. Theabrasive article of claim 10, wherein each distal region is curvilinear.13. The abrasive article of claim 9, wherein each base is aparallelogram.
 14. The abrasive article of claim 13, wherein none of thesides of the parallelogram is parallel to an edge of an article uponwhich the abrasive array is disposed.
 15. The abrasive article of claim9, wherein for each unit, its respective distal region, when projectedon to a plane that is coplanar with its respective base, falls withinthe periphery of the base.
 16. The abrasive article of claim 9, whereinconsecutive bases do not abut.